1. Field of the Invention
The present invention relates to sealing devices and turbo machines, and more specifically to a sealing device that controls a leakage flow in a clearance passage defined between the rotor and stator of a turbo machine and to a turbo machine with the sealing device.
2. Description of the Related Art
In turbo machines such as steam turbines, gas turbines, and centrifugal compressors, to prevent working fluid from leaking along a rotating shaft (a rotor) from a casing (a stator) enclosing the rotating shaft, a labyrinth seal is often provided in a clearance passage between the rotating shaft and the casing. The labyrinth seal typically has a plurality of sealing fins in the axial direction of the rotating shaft. The labyrinth seal has chambers defined between the sealing fins along the outer circumferential surface of the rotating shaft. The chambers cause a pressure drop in the leakage flow of the working fluid flowing down in the labyrinth seal. This pressure drop controls a leakage quantity.
In the turbo machine with such a labyrinth seal, if a leakage flow (a swirl flow) having a velocity component in the circumferential direction of the rotating shaft flows into the labyrinth seal, vibrations of the rotating shaft tend to increase. A sealing device is proposed as a technology for suppressing such unstable vibrations of the rotating shaft in JP-2012-7594-A. The sealing device incorporates a stepped portion on the outer circumference of an impeller (a rotor), the stepped portion being reduced in diameter from the higher pressure side toward the lower pressure side. In addition, the sealing device incorporates a plate-shaped swirl breaker on the lower pressure side of the stepped portion of the impeller (the rotor) and on the higher pressure side of the labyrinth seal, the swirl breaker extending radially inwardly from the casing (the stator) and facing the rotational direction of the rotor. In this way, the sealing device prevents the swirl flow from going into the labyrinth seal.